Generally, a cooking table on which a heating device such as an electric heater or a gas range for cooking such as boiling or baking through an application of high-temperature heat to food is disposed is provided in a kitchen.
In this case, in a process of heating food to be cooked which is heated by a high temperature of the heating device disposed on the cooking table, contaminants such as smoke, odor, oil vapor, and the like are generated. Such contaminants may float due to the heat and diffuse throughout a kitchen or an entire room, and the diffused contaminants provide an unpleasant odor which causes aversion. Specifically, in a closed kitchen, these contaminants become factors that degrade the concentration of workers and harm the health of the workers.
Accordingly, a range hood for discharging contaminants such as smoke, odor, oil vapor, and the like which are generated when food is cooked to the outdoors is provided in a kitchen.
Such a range hood may include a main body which forms an exterior of the range hood, a fan which sucks air into the main body and generates airflow for discharging the air to the outside, a filter which is installed in the main body and filters the air sucked into the main body, and a pipe or duct which forms a path for discharging the air sucked into the main body through the filter to the outside.
Since a predetermined power is supplied to an alternating current (AC) motor used in a conventional fan for each airflow mode, it is impossible to control a rotational speed of a fan. Conversely, a brushless direct current (BLDC) motor has an advantage in that a rotational speed of a fan may be controlled.
In the case of a conventional BLDC motor, initially, the motor was controlled by a method of controlling a rotational speed at a constant speed for each airflow mode. However, in the case of a rotational speed control method (i.e., a so-called revolutions per minute (RPM) control method), when there is a flow resistance (a load) in an outlet of a hood, airflow generated in the hood is decreased even when the fan rotates at the same rotational speed.
Specifically, in the case of the RPM control method, airflow generated by the BLDC motor may be greater than airflow generated by an AC motor when there is little flow resistance in the outlet of the fan. However, when a flow resistance of a certain level or more is generated, use of the AC motor results in greater airflow (see FIG. 4).
In consideration of the above characteristics, by applying a method of controlling a fixed current in a BLDC motor, it is possible to control airflow to be the same as or greater than that of an AC motor even when high or low flow resistance is generated in an outlet of a fan. However, in this case, since there is no difference in efficiency of airflow generation between an AC motor and a BLDC motor (see FIG. 4) as the flow resistance in an outlet of a fan is increased, it is unnecessary to apply a BLDC motor which requires complicated control thereto.
Meanwhile, an airflow mode of a range hood is set to generate airflow intended by range hood designers. The airflow is determined in consideration of a structure of a main body, a fan, and a filter constituting a product. However, a structure of a duct behind the fan of the range hood may not be controlled by the designers of the range hood. Therefore, when an installation structure or environment of the range hood is changed (i.e., when the range hood is installed in another apartment or the like), the airflow intended by the designers is not generated in the airflow mode of the range hood installed in the corresponding environment and this may lead to a degradation of performance of the product.
Therefore, even when the installation environment of the range hood is changed, the BLDC motor should be controlled to generate the airflow intended by the designers so that the range hood may efficiently operate to meet the designed intention thereof. Also, these characteristics are not limited to the range hood.